This invention relates to carbonate polymer compositions, and in particular to carbonate polymer compositions which exhibit flame resistant properties.
Carbonate polymers derived from reactions of dihydroxyorganic compounds, particularly the dihydric phenols, and carbonic acid derivatives such as phosgene, have found extensive commercial application because of their excellent physical properties. These thermoplastic polymers are suitable for the manufacture of molded parts wherein impact strength, rigidity, toughness, heat resistance and excellent electrical properties are required.
Unfortunately, however, these polymers exhibit a brief but definite burning time when contacted with an open flame. More importantly, as is often the case, the carbonate polymers contain stabilizers and other additives which are often more combustible than the unmodified carbonate polymer. In particular, rubber-modified polycarbonates are commercially important examples of a carbonate polymer containing a more combustible additive. Rubber is incorporated into polycrbonate to improve the low temperature and sharp notch (i.e., 5 mil Izod) impact resistance. When ignited these rubber components give off flammable vapors. As a result, the modified carbonate polymers frequently exhibit substantially poorer resistance to combustion than does the unmodified carbonate polymer.
In attempts to increase the combustion resistance of carbonate polymers including the modified forms thereof, it has been a common practice to employ monomeric phosphites, phosphoric acid esters, thiophosphoric acid esters containing halogenated alkyl radicals and halogenated organic compounds into the carbonate polymer. However, in order to obtain any significant improvement in combustion resistance, these additives are frequently employed in such large quantities that they often adversely affect many of the desirable physical, optical or mechanical properties of the carbonate polymer.
In view of the deficiencies of conventional fire retardant carbonate polymer compositions, it would be highly desirable to provide a carbonate polymer composition exhibiting good toughness and having improved resistance to burning when exposed to an ignition source.